Near-infrared spectroscopic method for assessing the tissue oxygenation state of living lung

To quantify changes in tissue oxygenation of pathologic lungs, we applied a novel method using near-infrared spectroscopy (NIRs). In in vitro experiments, we assayed the effect of photon scattering on the absorption spectra of an in vitro system simulating structures of lung, which consists of test tube containing air in hematocrit tubes and red blood cell suspension with various predetermined hemoglobin concentrations. It was determined that photon scattering of the tissue containing air did not affect the absorption in the NIR region. In in vivo experiments, we tested the applicability of the NIRs technique in rat lungs under the following conditions: (1) hypoxic loading; (2) administration of an inhibitor (NaCN) of the mitochondrial respiratory chain; (3) hemorrhagic shock. We found that: (1) Changes in hemoglobin oxygenation state in the lung measured by NIRs depended on inspired oxygen concentrations; (2) NaCN-induced reduction of cytochrome oxidase a,a3 in the lung was observed; and (3) Total hemoglobin levels in the lung decreased after bleeding. Changes in the hemoglobin oxygenation state and cytochrome oxidase redox state in the lung were determined using the least-square-curve fitting for NIR absorption spectra. Our NIRs technique was capable of assessing the hemoglobin oxygenation and cytochrome oxidase redox state in the lung.